Diffusion of benzene through the beta zeolite phase

Abstract

Molecular dynamics simulations are used to calculate the self-diffusion coefficients, orientation autocorrelation function, activation energy for diffusion, adsorption energy, snapshots showing spatial distribution, and radial distribution functions of benzene in the all-silica form of beta zeolite. The aim is to understand the effects of temperature and loading on the diffusion of benzene guest molecules and their dynamical behavior in beta zeolite. Simulations of benzene in beta zeolite have been performed between 300 and 900K with loadings of 1, 2, and 3 molecules per unit cell. Self-diffusion coefficients increase from 300 to 900K and with increased loading, self-diffusion and activation energy of benzene diffusion decreases. The mean-square displacement (MSD) for the center of mass of the benzene molecules in the x, y and z-directions shows that the motion of benzene is not homogeneous in the zeolite framework and there is anisotropic translational diffusion for benzene in the zeolite. The MSDs in the x- and y-directions are much larger than in z-direction which is a reflection for the anisotropic microscopic structure of the zeolite. The velocity autocorrelation functions for benzene are also calculated and interpreted in the different temperatures. The adsorption energy of the benzene guests calculated from these simulations is in good agreement with quantum chemical results.